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CU, MIT breakthrough in photonics could allow for faster and faster electronics

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From left, Jeff Shainline, a postdoctoral researcher; Milos Popovic, an assistant professor in ECEE; and Mark Wade, a graduate student, discuss the silicon wafer containing the photonic-electronic microchips they designed.

A pair of breakthroughs in the ﬁeld of silicon photonics by researchers at CU-Boulder, the Massachusetts Institute of Technology and Micron Technol­ogy Inc. could allow for the trajectory of exponential improvement in micro­ processors that began nearly half a century ago - known as Moore's Law - to continue well into the future, allowing for increasingly faster electronics, from supercomputers to laptops to smartphones.

The research team, led by CU-Boulder researcher Milos Popovic, an as­sistant professor of electrical, computer and energy engineering, developed a new technique that allows microprocessors to use light, instead of electrical wires, to communicate with transistors on a single chip, a system that could lead to extremely energy­-efﬁcient computing and a continued skyrocketing of computing speed.

First laid out in 1965, Moore's Law predicted that the size of the transis­tors used in microprocessors could be shrunk by half about every two years for the same production cost, allowing twice as many transistors to be placed on the same-­sized silicon chip. The net effect would be a doubling of computing speed every couple of years.

This exciting innovation could mean Moore's Law could be extended into the future.

The projection has held true until relatively recently. In the last half-­dozen years, microprocessor manufacturers, such as Intel, have been able to con­tinue increasing computing speed by packing more than one microprocessor into a single chip to create multiple "cores." But that technique is limited by the amount of communication that then becomes necessary between the microprocessors, which also requires hefty electricity consumption.

Using light waves instead of electrical wires for microprocessor communi­cation functions could eliminate the limitations now faced by conventional micro­processors and extend Moore's Law into the future, Popovic says.

Optical communication is already the foundation of the Internet and the majority of phone lines. But to make optical communication an economically viable option for microprocessors, the photonics technology has to be fabri­ cated in the same foundries that are being used to create the microprocessors. Photonics have to be integrated side by side with the electronics in order to get buy­-in from the microprocessor industry, Popovic says.

In two papers published in Optics Letters with CU-Boulder postdoctoral researcher Jeffrey Shainline as lead author, the research team reﬁned their original photonic­electronic chip further, detailing how the crucial optical mod­ulator, which encodes data on streams of light, could be improved to become more energy efﬁcient. That optical modulator is compatible with a manufac­turing process used to create state­-of­-the-­art multicore microprocessors such as the IBM Power7 and Cell, which is used in the Sony PlayStation 3.

The CU-­led effort is a part of a larger project on building a complete photonic processor­-memory system, which includes research teams from MIT, Micron Technology and the University of California, Berkeley. The re­ search was funded by the Defense Advanced Research Projects Agency and the National Science Foundation.